Arteriogenesis (collateral blood vessel growth) is the most important endogenous mechanism of compensation for an arterial stenosis or occlusion. The driving force is a pressure gradient, for example through a stenosis or an AV-shunt, which initiates an increased blood flow through the collateral arteries in the areas of hypoperfusion. Arteriogenesis is induced by flow, namely by an increased shear stress which act on endothelial cells. Diseases related to ischemic arterial blockage represent the most common cause of death in the western world (Lloyd-Jones, Adams et al. 2009). The most common causes of stenosis or occlusive diseases of the main arteries of the brain, the heart or the periphery are progressive atherosclerotic modifications of the blood vessels. The possibilities for treating such diseases are at the present time very limited, whereby the therapies on offer are often unsatisfactory (Schiele, Niehues et al. 2000). Angioplasty (balloon dilatations) and bypass operations are the only methods of treatment available in clinics at the present time. An angioplasty can however only be applied in a case of an arterial obstructive or occlusive disease (for example ischemic heart diseases) and as a consequence leads to an increased risk of a restenosis. Bypass surgeries are in any case only applicable for certain arterial obstructive or occlusive diseases and are associated with the disadvantage that an invasive intervention is necessary. New therapeutic strategies are therefore particularly relevant when considering how to treat and to avoid vascular obstructive or occlusive diseases. A pharmaceutical stimulation of arteriogenesis (the concept of growing a biological bypass) represents enormous therapeutic potential and a very promising method in treating or preventing arterial obstructive or occlusive diseases (Love 2003). The present invention therefore relates to the modulation of arteriogenesis and flow-induced collateral blood vessel growth (FIG. 1).
The vascular system is organized in a highly complex manner. In order to ensure the essential functions of distributing oxygen and nutrients, the vascular system is constantly undergoing reconstruction. The reconstruction of blood vessels differs between arteriogenesis on the one hand and angiogenesis on the other hand.
In the context of the present invention it is important to distinguish between arteriogenesis and angiogenesis. Angiogenesis relates to the outgrowth of new capillaries from previously existing vessels. This relates specifically to the growth of new vessels (capillary sprouting). The present invention does not relate to modulation of neo-vascularisation (such as angiogenesis) but rather to modulation of arteriogenesis.
The diameter of an artery is actively increased in arteriogenesis. This mechanism does not deal with a passive dilatation, rather an active reconstruction of the vessel including the degradation of the extracellular matrix and a proliferation of artery cells (endothelial cells and smooth muscle cells), in order to achieve the required structure for a larger artery. The end result of arteriogenesis is that a pre-existent small artery grows into a large functional conductance artery. The initial stimulus for arteriogenesis is a change in the shear stress of the endothelial layer (not ischemia), which occurs through an increase in the blood flow through an artery.
It is therefore important to note that the present invention relates to arteriogenesis, the mechanism of which is fundamentally different from the mechanism of angiogenesis (Schaper 2009).
Previous studies have focused on the investigation of angiogenesis, whereby VEGF has been identified as a major regulator. Previous studies on rabbits, in which the femoral artery has been removed, show that under these hypoxic conditions VEGF is strongly up-regulated (Takeshita, Zheng et al. 1994). Additional application of the specific endothelial mitogen VEGF can stimulate artery growth. Such studies however do not distinguish between the outgrowth of capillaries (angiogenesis) and the mechanism related to the collateral growth of arteries (arteriogenesis). Angiogenesis occurs directly in the ischemic area and hypoxic conditions lead to the local production of VEGF. VEGF functions primarily as a mitogen for endothelial cells. However, arteriogenesis requires the reconstruction of endothelial cells, smooth muscles cells and a highly regulated end complex reconstruction of the extracellular matrix. In the case of an arterial obstructive or occlusive condition angiogenesis alone does not lead to a significant improvement in perfusion (Zadeh and Guha 2003, Storkebaum and Carmeliet 2004, Wang, Killic et al. 2005).
B1-receptor agonists are also known for modulating angiogenesis (Emaueli, Circulation, 2002), although only in relation to the outgrowth of capillaries (angiogenesis) and not in relation to modulation of the growth of collateral arteries (arteriogenesis).
In addition to flow-induced reconstruction, the migration of leucocytes plays a decisive role in arteriogenesis. Leucocytes, especially monocytes, produce inflammatory cytokines and growth factors, which are of significant importance for the remodeling of an artery. Such a remodeling leads to the enlargement of an arteriole into an artery with an outward growth of the artery lumen (positive outward remodeling). Arteriogenesis is therefore the most important endogenous compensatory mechanism for the maintenance of a stable blood flow in the case of a stenosis (mechanism of a biological bypass, FIG. 1). Arteriogenesis however generally does not occur in the ischemic region but rather in regions proximal to the occlusion and therefore effects the bypass circulation which provides blood supply to the distal hypoperfusion area (FIG. 1) (Pipp, Heil et al. 2003).
A schematic curve demonstrates the biological importance of arteriogenesis (FIG. 2a). Angiogenesis produces many new capillaries with a small diameter where as arteriogenesis enlarges the diameter of already existing arteries (FIG. 2b). The Hagen-Poiseuille rule demonstrates the relationship between blood flow and artery diameter and shows that the blood flow is enhanced by an exponential factor of 4 in relationship to the radius (FIG. 2b). According to this rule a minimal change in artery radius leads to significant improvements in perfusion. Comparable improvements in perfusion can not be achieved through the growth of many new small capillaries, as is the case in angiogenesis.
Previous studies have shown that collateral artery growth can be stimulated by an increase in blood flow (specifically an increase in the shear stress of the endothelial cells) or through the application of cytokines such as a GM-CSF (Buschmann, Busch et al. 2003). In a stroke or apoplexy model in the rat is has been shown that stimulation of arteriogenesis via the application of GM-CSF leads to an increase of the haemodynamic reserves of the brain (Schneeloch, Mies et al. 2004). Through the application of GM-CSF the ischemic region in an experimentally induced stroke could be significantly reduced. The stimulation of arteriogenesis is therefore an effective strategy for the treatment and/or prevention of ischemic obstructive or occlusive conditions, in addition to heart attacks and strokes.
Factors such as GM-CSF have been tested for their therapeutic stimulation of arteriogenesis (van Royen, Schirmer et al. 2005). The bradykinin signaling pathway has however not been examined in the prior art for its role in arteriogenesis, although its function as a vasodilator (antagonist of the Renin-angiotensin system) and its stimulatory effect in neo-vascularisation (Emanueli, Bonaria Salis et al. 2002) is known.
Bradykinin receptor 1 (B1R) and bradykinin receptor 2 (B2R) belong to the kallikrein-kinin system (KKS), which also contains the proteins kallikrein and kininogen. Kininogen is a substrate of the KKS and is enzymatically cleaved by kallikrein, through which a number of kinins are released.
Bradykinin, T-kinin and kallidin all belong to the kinin group. These proteins can be digested at their C terminus by a carboxypeptidase and can therefore be transformed to Des-Arg9-bradykinin and Des-Arg10-kallidin. Bradykinin, T-kinin and kallidin impart their signaling effect via the B2-receptor and Des-Arg9-bradykinin and Des-Arg10-kallidin via the B1-receptor (FIG. 3). All components of the kallikrein-kinin system can be produced in the artery wall. The bradykinin receptors in the artery walls can be expressed in either the endothelial cells, the smooth muscle cells or in leucocytes. A signaling effect via the bradykinin-receptors leads to vasodilatation, cell proliferation, inflammation and the production of various cytokines.
The effect of B1R and B2R agonists and antagonists on angiogenesis, which is the formation of new blood vessels, has been disclosed in the prior art. The relationship between angiogenesis and the bradykinin signaling pathway has also been investigated (Stone et al., 2009). It is known that treatment with agonistic substances of B1R and B2R leads to the promotion of angiogenesis and the formation of new vessels (WO 02/17958 A1). B1R and B2R antagonists have also been used for treating cerebral ischemic injury, arteriosclerosis, pain and inflammation (WO 98/06417, EP 0623350 A1, WO 2006/071775 A2).
Agonists of the B1R (such as increased B1R expression, peptides and various chemical derivatives of heterocyclic compounds) have been disclosed that may be useful in treatment of stroke patients, hypertension or heart failure (DE 10115668 A1, U.S. Pat. No. 6,015,818, WO 2004/069857).
Despite the extensive prior art surrounding the Bradykinin receptors and their role in angiogenesis, until the present time there has been no knowledge that connects Bradykinin receptor 1 (B1R) or bradykinin receptor 2 (B2R) with arteriogenesis.
Patients in need of stimulated or enhanced arteriogenesis, or patients who are at risk of suffering from disorders associated with an increased need for enhanced arteriogenesis, have long suffered through the lack of effective medicaments that target arteriogenesis. Similarly, patients with blood vessel malformation have been without effective treatment options, considering that until now no medicaments were known that could effectively reduce arteriogenesis in those patients where such treatment would be beneficial.
The pharmaceutical stimulation of arteriogenesis has previously been identified as exhibiting therapeutic potential and is a promising option for treating or preventing arterial obstructive or occlusive diseases or other conditions or disorders associated with defective blood flow (Love 2003). Despite this need, until now effective products and methods for modulating arteriogenesis were unknown.